A number of automobiles now provide wipers for rear windows where the rear window has a tendency to become deposited with contaminants and rain water that obscure the rear field of vision. These wipers are in many respects similar to conventional front windshield wipers in operation.
More specifically, a conventional window wiper typically has at least one pivotal wiper arm fitted with a rubber blade to effect a squeegee action when the wiper arm is pivoted through a wipe pattern across the window. The wiper arm begins at rest from a park position on the edge of the glass boundary of the window and intially traverses a park stroke to enter a reciprocating, pivotal motion through the wipe pattern. The wiper concludes its operation by traversing the park stroke in the opposite direction and returning to the park position. This sequence of motion is governed by a wiper motor and transmission which are conventional in the art.
It is often desirable to remove the wiper blade from the glass pane of the window during the park stroke. It is necessary to remove the wiper blade from the glass pane when the vehicle window is of the drop glass type, i.e. where the glass may be retracted within the body or door panel of the vehicle to open the window and may be extended into the window opening to close the window. This type of window must be fitted with a wiper which parks off the glass to permit window opening and closing.
It is also necessary to remove the wiper blade from the glass pane when the glass pane is included on a flip-out mechanism. In this situation, the rear window glass "flips out" from the top of the vehicle on which it is hingedly attached.
The air and liquid seal or molding which is generally provided between the window glass and frame to provide a seal between the two requires that the window glass be recessed relative to the frame. As a consequence, any wiper fitted to such a window must be capable of movement with two degrees of freedom, i.e. through the dimension of recess and through the wipe pattern of the glass surface.
It is known to provide a special inclined surface or a cam face which cooperates with the arm of a windshield wiper mechanism in such a manner that when the arm and thereby a blade thereof moves to a rest or park position the blade is lifted off the windshield to free it of stress. However, in many instances space limitations make it difficult to provide such an inclined cam face, or else require that the cam face be at a location on the vehicle which presents unacceptable problems either from a point of view of aesthetics or for operational considerations. For instance, the location must be such that the windshield wiper arm does not freeze to the cam face in cold weather conditions.
Prior patents disclose windshield wiper mechanisms which include cams which guide the wiper arms from a working position where the wiper blade contacts a window pane to a rest or park position where the wiper blade is moved away from the surface of the window pane and is disposed in an out-of-the way position relative to the window. For example, the U.S. Patent to Dunhill et al, U.S. Pat. No. 4,091,494 discloses an adjustable mounting with a pair of threaded fasteners having a guide or cam which projects outwardly from the pane of the glass. The cam functions like a ramp to guide the wiper blades through the park stroke. Likewise, the U.S. Patent to Mainka U.S. Pat. No. 3,604,048 discloses a wiper system including guide means in the form of a cooperating cam and follower to impart axial movement to the wiper arm to lift it off the windshield in a rest position.
The U.S. Patent to Palma U.S. Pat. No. 4,310,943 discloses a window cleaning system for a rear, drop glass, vehicle window, e.g. of the type on a utility station wagon. The system includes one or more wiper arms disposed on the window frame above the glass pane. Each wiper arm has a pivotal axis for rotation of the arm from a park position through a wipe pattern. The arm enters the wiper pattern through a park stroke in which the arm is brought downward and inward from the park position on the frame; the exit from the park stroke is by mutually opposite movement. Each wiper arm is guided through the park stroke by guide means as it is driven by a wiper motor. The guide means takes the form of a cam and follower arrangement. The cam is preferably formed as a projecting guide finger having a shape or configuration defining the park stroke. The follower is formed as a central offset segment of the wiper arm which engages and is guided by the projecting guide finger. Specifically, the finger guides the travel of the wiper arm through the park stroke in both transverse axes of travel, i.e. vertically and horizontally.
Other wiper mechanisms generally of the type to which this invention relates are disclosed by the U.S. Patent of Rappl U.S. Pat. No. 2,284,844, Forbush et al U.S. Pat. No. 3,112,510; Trzebinski U.S. Pat. No. 3,224,026; Scinta U.S. Pat. No. 3,452,384; Druseikis U.S. Pat. No. 3,415,132; Omlie et al U.S. Pat. No. 3,505,702; Sargent et al U.S. Pat. No. 3,545,027, Skahill U.S. Pat. No. 4,266,315; Carpenter et al U.S. Pat. No. 3,107,383; Burke U.S. Pat. No. 1,787,894; Oishei U.S. Pat. No. 1,826,672; Oishei U.S. Pat. No. 1,937,160; Dangler U.S. Pat. No. 3,110,920 and O'Steen U.S. Pat. No. 4,040,141.